In general, retinoscopy is an examination method in which certain light beams in front of an examinee are projected into an eye and a pupil of an examinee so that an examiner observes a refractive state of reflected light beams which are reflected from the pupil to find a far point location of the eye of the examinee.
A tool used for the retinoscopy is a retinoscope, and types of retinoscope include a spot retinoscope and a streak retinoscope. Here, the streak retinoscope is widely used since the spot retinoscope has difficulties in examining astigmatism and axis.
As shown in FIG. 1, in a refraction examination using a conventional retinoscope, a distance for an optometric examination between an examinee and an examiner is fixed in a range of 50 cm to 67 cm, a rack lens is located at about 12 mm in front of the eye of the examinee, and then the examinee is instructed to keep the eye on an eye chart from a long distance (5 m). At this point, the examination has to be performed in a state in which the examinee is keeping the eye on the eye chart from a long distance to minimize intervention of control. Accordingly, the examiner has to make an examination at a tilted angle, thus not blocking a line of sight of the examinee. That is, while the line of sight of the examinee passes by the ear of the examiner, the examiner uses his or her right hand and right eye when examining the right eye of the examinee, and uses his or her left hand and left eye when examining the left eye of the examinee, thereby minimizing dislocation of the line of sight as much as possible.
A refraction examination using such a conventional retinoscope has a great effect of suppressing the intervention of control of the examinee and serves as a useful examination method when communication between the examiner and the examinee is not smooth.
However, if dislocation of the line of sight of the examiner and the line of sight of the examinee is large, an error occurs as a measurement is taken away from the center of a cornea. Hence, there has been a problem in that the larger the error, the harder it is to perform an accurate examination.
Further, since the examiner has to observe reflected light beams reflected from a small pupil of the examinee at a distance for an optometric examination in a range of 50 cm to 67 cm, it is not easy to observe the reflected light beams. In particular, if the examinee has a small pupil, it is harder to observe the reflected light beams, thereby increasing eye strain of the examiner. Further, when the examiner is old or has poor vision, an accurate examination is difficult to be performed.
Further, since the examiner has to use his or her right hand and right eye when examining right eye of the examinee and has to use his or her left hand and left eye when examining left eye of the examinee, the examiner feels uncomfortable with examination posture when examining the other side, depending whether the examiner is a right-hander or a left-hander. There has also been a problem in that the examiner with a tremoring hand cannot perform a refraction examination.
Further, there has been a problem in that it is hard to maintain a predetermined distance for an optometric examination with the examinee. Here, diopter of a correction lens is 2 D when the distance for an optometric examination is 50 cm, and 1.5 D when the distance for an optometric examination is 67 cm. While applying diopter with a distance for an optometric examination of 50 cm, if an actual distance for an optometric examination is 50 cm or more or 50 cm or less, an error of 0.25 D unit may occur since a displacement unit of the lens is 0.25 D. Such an error reduces accuracy of the examination, and therefore, it is important to maintain the predetermined distance for an optometric examination.
Further, there is a problem in that it is hard to maintain a predetermined distance between the eye of the examinee and a rack lens located in front of the eye. For example, in the case of a retinoscopy lens with 7.00 D, even though location of the lens changes by only 5 mm, a change of 0.25 D occurs. Therefore, since a predetermined distance between the eye and the rack lens has to be maintained at 12 mm, accuracy of the examination is reduced when the rack lens is located in front of the eye of the examinee by roughly estimating distance.
While such a manual refraction examination has a great effect of suppressing the intervention of control of the examinee and serves as a useful examination method when communication between the examiner and the examinee is not smooth, location adjustment and an examining posture are very difficult, and considerable effort and time are required to be skillful with the examination method. In addition, since the examination is performed manually, an error occurs easily, and further, an accurate examination value cannot be obtained since the examination is done in a subjective manner that can only be performed by a skilled person. Further, it is inconvenient that the examination has to be performed with the rack lens changing in the course of the examination.
Recently, an auto-refractometer has been provided to measure refractive errors simply and rapidly.
The auto-refractometer has advantages of diagnosing refractive errors of an examinee and finding prescribed power for correcting the refractive errors based on the diagnosed information rapidly and precisely, however, due to intermittent error occurrence, the retinoscope is still used at the same time. Therefore, the retinoscope is still a very important examining tool in optometry.